The present invention is related to electronic circuits, and more particularly to a charging circuit for blocking reverse currents.
Many portable electronic devices utilize a rechargeable battery to provide power. These devices include computers, cellular telephones, pagers, radios, and the like. While there are many types of rechargeable batteries used today, including nickel cadmium and nickel metal hydride, lithium ion batteries have become a popular choice. Lithium ion batteries are typically smaller and lighter than other rechargeable battery types while charge capacity is increased.
Typically, to charge a battery, a battery is connected to a charger that is plugged into an AC outlet. During the time the charger is plugged in and the device is in the charger, an indicator light on the charger generally shows the charging status of the battery. For example, the indicator light may flash when the battery is charging and be on constantly when the battery is fully charged. If the user removes the charger plug from the wall with the device still in the charger, the stored charge of the battery may be reduced.
Even when the battery is not being used within an electronic device, energy may be lost due to the internal circuitry contained within the battery. If the battery is discharged too deeply, the life cycle of the battery may be reduced. For example, the battery may slowly discharge when the battery is connected to the charger but the charger is not connected to the power source. The amount of energy lost between the time when the battery is connected to a charger that is not connected to a power supply and when the battery is connected to a power supply can result in the battery being deeply discharged. Potentially, the battery may not be able to store energy if discharged too deeply.
The present invention is directed at providing an apparatus that is integrated onto a battery charging integrated circuit (IC) for blocking reverse discharge currents of a rechargeable battery.
According to one aspect of the invention, a PMOS device prevents reverse currents from draining the battery. The PMOS device is activated when a light load is detected on the cell and the cell is not being charged. The light load detected may occur when the device is connected to the charger but the charger remains disconnected from a power source. A sense circuit is also used to help determine when the charger is not connected to the battery.
According to another aspect of the invention, the reverse blocking function apparatus removes an external component from a conventional charger and integrates the function of the component onto the battery charging IC.
According to yet another aspect of the invention, the apparatus uses a lower compliance xe2x80x9conxe2x80x9d voltage as compared to a conventional battery charger circuit that is intended to block reverse currents. For example, the reverse blocking function apparatus integrated onto the battery charging IC requires less headroom as compared to a Schottky diode.